Macrophage activation during experimental murine brucellosis: a basis for chronic infection

Evidence is presented that the chronicity of infection in CBA mice after injection of Brucella abortus 19 is related to a number of factors: (i) the relative resistance of B. abortus to macrophage killing, which allowed some bacteria to survive the peak of macrophage activity occurring at 14 days; (ii) the decline in macrophage activity thereafter (this decline was related in part to the presence of fewer bacteria to stimulate the bactericidal activity and also to specific, active suppressor mechanisms not identified in this study); and (iii) the insensitivity of the persistent Brucella organisms to activated macrophages. This was not due to a selection of genetically resistant bacteria, but possibly to their inaccessibility, either within "incompetent" macrophages or outside macrophages altogether.